1. Technical Field
The present invention relates to a method of manufacturing a laminated substrate, and a laminated substrate. More specifically, the present invention relates to a method of manufacturing a laminated substrate, and a laminated substrate using high-hardness substrates having a hardness of equal to or more than 150 GPa in Young's modulus. In the designated countries where incorporation of documents by reference is approved, the content described in the specification of the following patent application is incorporated into the present patent application by reference, and will be regarded as a part described in the present specification. Japanese Patent Application No. 2006-043281 Date of filing: Feb. 21, 2006
2. Related Art
In recent years, a SOI substrate in which a semiconductor thin film typified by silicon is formed on an insulating material is increasingly used as a substrate for an energy saving device. The SOI substrate is typically formed by depositing a silicon support (handle) substrate, forming a silicon oxide film thereon, and forming a silicon thin film thereon as a top layer.
Meanwhile, some special SOI substrates may use a clear substrate such as sapphire as the handle substrate in order to be used for a high-frequency device. The reason is that the clear substrate as the handle substrate has a high transparency, a high heat conductivity and a low dielectric constant. Such substrate is referred to as Silicon on Sapphire: SOS, in which the silicon layer typically heteroepitaxially grows on the sapphire (e.g. see Patent Document 1). As a result, the silicon layer has many defects while growing due to difference of the lattice constant between silicon and sapphire.
A laminating method may be applied to the method for manufacturing such SOS. However, lamination requires a significantly high flatness (equal to or less than 0.5 nm rms). Therefore, when a hard material such as sapphire is used, the laminated interface has void defect since roughness and scratch remain on the surface after polishing.
Not only when sapphire is used, but also when other hard materials such as SiC (Young's modulus=about 250 GPa) and AlN (Young's modulus=about 300 GPa) are used, it is difficult to achieve a high flatness due to it's hardness, consequently, such hard materials are not suitable for lamination.
As described above, although the high-hardness substrates made of sapphire and SiC etc. have excellent characteristics such as heat-releasing characteristic and insulating characteristic, it is difficult to achieve a high flatness due to it's hardness, consequently, it is difficult to achieve a laminated substrate having a small defect density.
Accordingly, a method for manufacturing a laminated substrate has been required, which uses a high-hardness substrate for lamination to provide a substrate having a small defect density.
Patent Document 1: Japanese Patent Application Publication No. 10-83962
In view of the above described problems, the present invention is to provide a method of manufacturing a laminated substrate that provides a laminated substrate having a small defect density by using high-hardness substrates for lamination.